Invasive species reported in Bay Area hatchery for the first time

An invasive species seen for the first time in Lake Tahoe earlier this year could also pose a risk for a Bay Area fish hatchery that operates production and release programs for endangered coho salmon and threatened steelhead trout.  

New Zealand mudsnails, a species of tiny freshwater mollusk, were spotted inside an intake pipeline and aeration pond at Warm Springs Fish Hatchery near Lake Sonoma this summer, California Department of Fish and Wildlife officials said in a statement Friday. The snails were previously detected in other parts of the watershed, but had never been observed at the hatchery before. It’s causing concern for scientists, who worry the snails could displace native species like the salmon and trout, consuming up to half of their food resources, including aquatic insects such as mayflies, caddisflies and chironomids. 

“The detection levels so far have not been alarming, but we want to do everything we can to minimize the spread,” CDFW North Central Regional Manager Morgan Kilgour said in a statement. 

First discovered in North America in Idaho’s Snake River in 1987, the snails eventually spread to the Owens River in California in 2000, and officials believe further infestation was due to shipments of live sportfish and recreational activities. Because the tiny snails grow no larger than 4 to 6 millimeters long, or about the size of a grain of rice, it’s easy for them to go unnoticed as they attach to waders, shoelaces, aquatic vegetation and fishing gear to become transported by unsuspecting anglers and boaters. They can also disperse through “floating freely or on algal mats, or by surviving passage through fish guts,” per the CDFW.

Wildlife officials said the presence of New Zealand mudsnails have previously been identified at Dry Creek, which flows adjacent to Warm Springs Hatchery, and though the reason for the spread of the snails remains to be seen, they suspect the snails traveled to the hatchery through Lake Sonoma. In response, the CDFW said it is closely monitoring fish populations at the hatchery and has increased biosecurity measures there. Officials are also working with the U.S. Army Corps of Engineers, which operates the Russian River Coho Salmon captive broodstock program at the hatchery, and the National Oceanic and Atmospheric Administration to decide whether any changes in coho salmon release protocols will be necessary. 

People who visit the Russian River watershed should carefully inspect and decontaminate any equipment used in the water, wildlife officials said. If you do find any visible snails, remove them with a stiff brush and rinse off the equipment before freezing or completely drying it out (officials recommend doing so overnight for at least six hours). People should also never transport live fish or other plants or animals from one waterway to another.

When mudsnails were found in Lake Tahoe in September, Jesse Patterson, chief strategy officer for the League to Save Lake Tahoe, said that a new invasive species hadn’t been detected there in at least 15 years and called their presence “very uncommon.” He said they could potentially threaten the “delicate ecology” of the lake and impact its water clarity, while Dennis Zabaglo, aquatic invasive species program manager at the Tahoe Regional Planning Agency, noted food scarcity risks for native species similar to those faced by the salmon and trout at Warm Springs Fish Hatchery.

SFGATE Tahoe editor Suzie Dundas contributed to this report.